The invention is in the field of "smart" missiles and projectiles, and especially pertains to projectiles intended for use with airborne targets.
Projectiles in this area can be divided into two basic groups. First there are the self-propelled missiles which generally have on-board guidance systems and explosive charges. These are relatively complex arms items.
Second there are the artillery shells. Of the two, these are of course much simpler and generally less expensive. They are not self-propelled as a rule, although some designs incorporate trajectory correcting propulsive charges. Artillery shell projectiles are usually cheaper, simpler, and faster to deploy than missiles. They are the preferred form of terminal defence when defending, for example, a ship from in-bound missiles. Once one of these missiles is detected, there may be only a few seconds to destroy it, suggesting rapidly fireable artillery shells.
Additionally, because it is reasonable to assume that in many cases it will take several projectiles to destroy the incoming missile, it is desirable that they be inexpensive, simple, and quick to deploy and storable in reasonable quantities aboard the ship.
The challenge in producing an artillery projectile effective against incoming missiles lies in the need to make it "smart" so that it can correct its trajectory in real time. Because the incoming missile has its own evasive action program, no level of accuracy at the firing point will achieve contact. Incorporating trajectory-correcting capabilities in an artillery shell is complicated, compared to missiles, for two reasons. First, an artillery shell experiences thousands of G-forces when fired, so that any guidance mechanism must withstand this kind of shock. Second, whereas a missile is a relatively larger, more complex and more expensive device in which the incorporation of guidance systems may be done with relative ease, a shell is smaller, simpler, and cheaper, and does not traditionally have an on-board fuel supply to make propulsive corrections.
"Smart" artillery shells represent an area of some interest to the Pentagon at present. There have been a number of different schemes incorporated into the shells to effect trajectory correction. Most of these involve the detonation of propulsive charges on the sides of the projectiles responsive to information received from the mothership. Typical of this type of solution is U.S. Pat. No. 4,176,814 for a TERMINALLY CORRECTED PROJECTILE. U.S. Pat. Nos. 4,899,956 and 4,898,340 are also exemplary of this approach.
U.S. Pat. No. 4,399,962 on a WOBBLE NOSE CONTROL FOR PROJECTILES discloses a projectile with a nose which pivots at a hinge joint responsive to the firing of one of a multiplicity of charges at the joint area to deflect the nose, and thus deflect the missile toward its intended target. Intelligence is provided to the projectile from the mothership. There is no de-spinning, and the nose flips back and forth as the projectile rotates to maintain the appropriate net angle of attack of the nose.
Because most projectiles are spinning in flight for stability, it may be necessary in some designs to de-spin a portion of the projectile to provide a reference for trajectory correction. One approach to de-spinning is shown in U.S. Pat. No. 4,426,048.
In an article entitled "Atmospheric flight of a Variable-Bend body" in the JOURNAL OF GUIDANCE AND CONTROL, Volume 2, Number 5, September-October 1979, Page 382, the inventor and a co-author discuss the prospect of a bentbody projectile guidance technique dubbed "switchtail" technology. The theoretical aspects of switchtail techniques were investigated, but the article stopped short of describing how to actually produce a functional projectile using switchtail control force reduction theories.